Telephone system



March 29, 1938- E. P. G. WRIGHT ET AL 2,112,549

TELEPHONE SYSTEM Filed June 11, 1936 4 SheetsSheet l 'K kzE'l lkar'l lAK5 v ERG. WRIGHT AKGQ I 'WENTORS GZCIHARTLB ATTORNEY March 29,. 193 8.E. P. G. WRIGHT a? AL TELEPHONE SYSTEM 4 Sheets-Sheet 4 ERGWR/GHT ByG.C.HAR7ZEV wge ua Filed June 11, 1936 ATTORNEY Patented Mar. 29, 1938UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Application June 11, 1936,Serial No. 84,640 In Great Britain June 21, 1935 15 Claims.

This invention relates to telephone systems and more particularly,though not exclusively, to equipment for use in setting up long-distanceor toll connections.

The nature of the invention will be understood from the followingdescription of certain embodiments thereof.

It is intended to provide a combined line and recording (C. L. R.) tollservice entirely without plugs and cords. Each position is equipped withlinks having talking and monitoring keys and supervisory lamps, but theusual plugs are replaced by automatic switching apparatus. The switchingapparatus can be controlled either by dials on the operators positionsor by key sender equipment. Access is provided by means of the automaticswitches to all toll routes, to the local exchange equipment, and tomiscellaneous circuits such as test desk information and enquirypositions, etc.

Types of positions There are two principal types of positions, namelyinward and outward. The link circuits of the inward positions areconnected at one end to trunk line finders which can search for and pickup incoming calls, and at the other end to toll first selectors whichare the first switches in the automatic switch train giving access tothe various toll routes and the local exchanges. Each operator has up tofifteen inward links on her position, each one having a listening keyand monitoring key, calling and called supervisory lamps, and a busylamp. The associated position circuit contains the various keys requiredto control the completion and supervision of the connection, includingkeys for ringing both ways, splitting and releasing either way, togetherwith the digit keys required to control the key senders.

The outward positions are arranged to provide C. L. R. outward services,and also to act as toll or point-to-point positions. They are fittedwith two types of link circuits; the first is connected to a finder atone end, which searches for incoming calls on the record circuits, andat the other end to a toll first selector; while the second kind of linkis connected at both ends to toll first selectors via selector finderswhich are introduced to cut down the number of first selectors required.

The C. L. R. links have a special feature whereby the first level of thefinder is connected, not to incoming record circuits, but to toll firstselectors. Normally, the finder will not search over this level but canbe made to do so under control of a key in the operator's positioncircuit so that, when required, the link may be used for point-to-pointWork, or for the establishment of delayed calls. It is likely that thisfacility will be of considerable use in enabling the operator to releasethe calling side of the link and reverse the call should the 5 callingparty for any reason have become disconnected during the time in whichthe operator has been waiting for the forward connection.

Method of operation Apart from the delayed search facility describedlater on, the method of operation on various classes of call is asfollows:

(A). Inward calZs.-An inward call arriving on a toll line circuitestablishes a calling condition to 15 the.allotters which control themovement of the trunk line finders. These allotters will select asuitable link circuit for handling the call, and will cause theassociated finder to search for and seize the toll line circuit. Theprinciple of distribution '20 governing the movement of the allottersisthat calls shall be distributed to the various positions in rotation,except in so far as this is rendered impossible either by reason ofthere being no free links on a given position or if the position due to25 receive the next call is still testing busy owing to the operator nothaving cleared the sender from the preceding call. This latter conditionmay, of course, arise if the operator has difliculty in dealing with acall such, for instance, as a. per- 30 sonal call in which difliculty isexperienced in locating the wanted party.

When the inward link seizes a toll line circuit, a flicker condition isestablished on the calling supervisory lamp. The operator will answer bythrowing her listening key, and this process will cause the senderfinder associated with the position to pick up a free sender. At thesame time, the link circuit is connected to the operators positioncircuit. The operator will ascertain the particulars of the requiredconnection, and will immediately set up the required digits on her keystrip. The sender will then transmit the required digits to theautomatic selecting equipment, and in the case of a call terminatinglocally in an automatic exchange, this will actually give connection tothe wanted subscriber. In the case of a through call to another tollline, the automatic switchgear will simply select the toll line andthesubsequent ringing and supervisory work will be as for standard tollpractice.

During the time that the sender is transmittin the required digits, itconnects itself direct to the link via a by-path circuit so that theposition circuit is rendered available for the monitoring and theappropriate keys of the position circuit. To

release an established connection, the link circuit listening key isthrown, followed by the link re' lease key, it being assumed that thenormal routine for clearing the tolljline to the other operator haspreviously been carried out. The toll line signal is received as a'flicker signal on the supervisory lamp and this flicker condition in thetoll line circuit is automatica-ll-y'removed by the throwing of theassociated listening key. In

order to enable the operator to correct errors, or 1 to re-route callsin cases of difliculty, a forward release key isprovided whichre'leasesthe forward train but not the entire link; the operator may then; throwa key tore-introduce the sender and establish the call afresh. '(-B)-.Outward callS'.--The operating procedure on outward calls isessentially'the same except that' the operator will be required tofperform the customary 'docket'ing and'timing operations, and will inconsequence be unable to handle the same amount of trafilc. As aconsequence of this, the distribution scheme difiers from that'iforinwardcallsin that an perat r will signify her willingness to accept acall by throwing the key whereupon thelallotters will steer the calls tothe positions thus indicated: The C L. R. links are fitted with a deviceto enable them to be used as point-to-point links and, in' consequence,the position is provided with back and front release keys as well as akey 'torelease the entire link. The operator can, therefore, whenrequired, releasev the finder from a record circuit and by throwing a;special key cause the finder to select a toll first selector, and by theuse of her key sender can reverse the call to any desired term n n 1.(C'). Point-to-point calla-'I'hs-are delayed calls built up inaccordance with dockets, and they .will normally use the double endedlinks provided for this purpose. The operator will connecther key senderto the back, and front ends of the cord in turn, and will establishthereby a connection to the wanted parties or distant operators as thecase may be.

Group display lamps Both classes of positions are provided with a groupof lamps to indicate the groupor route of the incoming call. These lampsare lighted from an. additional bank of the line flnder, and,in order toavoid excessive splitting of the multiple, this bank is multipled over anumber of positions. This would normally result in confusion between theindications required by. the various positions, and to avoid this aflickerindication is given, the various positions being connected inturn, each for a'short period. The lighting of these lamps is controlledby. the keys on the position, so that the flicker control relaysneed notoperate except when the operator requires the display.

Delayed search Oneofthe major difliculties in securing emcient workingof a .C. L. B, toll board is due to the time taken by the operators inmaking repeated attempts to establish connections on a congested route.This difliculty is avoided by special arrangements for the groupselector circuits which search for a free toll line. The selec tors ofthese circuits are fitted with an additional wiper, the bank contactsassociated with which aretaken to a group congestion circuit and when atoll line. selector arrivesat the beginning of a group, beforecommencing a search it makes a test on this outlet for the specialcondition from the congestion circuit. If no toll line is available,this. condition will not be forthcoming, and the selector will refuseto, search, but will issue busy flash to the operator. The operator maynow restore her listening key in order to carry on with further calls.The busy flash will stop, but the link busy lamp will remain alight.When a toll line becomes free, the appropriate test condition isrestored to the control bank contacts, and this will cause the groupselector to transmit a flicker signal to the operator. If she decides toavail herself of the opportunity to complete the connection, she willthrow the listening key and this will cause the toll line selector tosearch over the group and select a free line. Special double testarrangements aremade so that in the event of two operatorssimultaneously attempting to seize the only available, junction, onlyone selector will commence to search and the other will proceed totransmit the flicker waiting signal again. Delayed Search may beprovided on a non-numerical forwardly hunting switch accessible from agroup selector instead of on the group selector itself. The groupcongestion circuit which con t'rols this operation is arranged for.special signaling on both-way routes so that when. calls are Waiting ontoll line selectors at each end of a both-way group, the congestioncircuits will allow them to be released in rotation in a sequencedependent on the time for which calls have been waiting at each end.

Special arrangement of senders The sender circuits are arranged toaccept the necessary code digits for the selection of an outgoing route,and also the numerical digits required for establishing aflocalconnection, or connection toa route which employs through dialing. Thesender will normally send the complete storage, but in the event ,of thetoll line selector on an out-dialing call failing to obtainimmediategaccess to a free junction, the sender will release withouttransmitting the numericals. When the operator, after the delayed searchoperation, eventually succeeds in obtaining a toll line, she will resetthe numericals in the sender, using a dummy code combination whichv thesender will not retransmit. 7

Another object of the invention is to provide means to permit a both-wayjunction to be used in such a manner that the period of delay ismaintained approximately equal for calls in each direction. It will beunderstood that where the number of junctions isrelatively small thedevice will control all the circuits but that in cases where the numberof junctions is greater, arrangements can be made to divide theavailable junctions into three groups, the first operating only in onedirection, the second operating in the reverse direction and thethirdoperating in either direction, according to the circumstances of. thetraflic. In the past it has been the practice for this control to beexercised by the operators at the terminations of the junctions.

On long-distance circuits, for which delay working has to be introducedfrequently, it is a common practice for the operators to pass a numberof calls in one direction and then a number of calls in the otherdirection, without paying particular attention to the waiting load oftraflic at either end. I

With more recent methods of toll switching it is becoming a practice toindicate to the operator one free junction in each group appearing onher position, and should all junctions be simultaneously in use, theparticular one which becomes free first will be immediately indicated atboth ends. Furthermore, no pro-vision is made to prevent the samejunction being indicated at both ends even when more than one junctionis free.

With C. L. R. working, a call is set up directly if a junction isavailable within, say, thirty seconds, but if a junction is notavailable in that time, the calling party is asked to hang up and aticket is made out and passed to a delayed call position. In the systemsemploying call storage, however, it is the practice to encourage theoperators to await a circuit becoming free for a longer time, and itwill be understood that if there'are a number of calls waiting at eachend of the junction there is a considerable danger that the junctionwill be seized at both ends simultaneously and the calls mutilated.

If toll dialing is employed it is important that such collisions shouldbe avoided, and the present invention also provides means to control thedirection from which calls should be accepted at the time of congestion.To accomplish this a recording device is associated with each end of agroup of junctions and a record is maintained of the product of thenumber of calls and the delay.

It may happen that if there is a preponderance of calls in onedirection, a single call in the reverse direction will have diflicultyin being handled in its correct turn. To compensate for this possibilitya further feature of this invention provides means whereby after anumber of calls in one direction preference is given to a call waitingin the reverse direction, and as the number of successive calls in onedirection increases the preference is also increased, tending to reversedirection.

In the accompanying drawings;

Fig. 1 shows the circuit of a non-numerical junction selector adaptedfor delayed calls;

Fig. 2 shows the circuit of a two-motion junction selector;

Fig. 3 represents, in schematic form, the circuits associated with bothends of a both-way junction group arranged to allot a junction fallingidle to the end at which congestion is worse;

Fig. 4 shows the relevant portion of a non-numerical trunk selector, ofthe kind shown in full in Fig. 1;

Fig. 5 shows a direction delay recorder; associated in multiple with allnon-numerical trunk selectors of a group;

Fig. 6 represents a delay counter circuit, associated with all thedirection delay recorders;

Fig. 7 represents a both-way trunk line circuit accessible from thetrunk selector;

Fig. 8 is an association circuit for connecting together a directiondelay recorder and a trunk line circuit as the latter becomes free;

Fig. 9 is a direction compensator and is individual to the directiondelay recorder of Fig. 5.

Fig. 1 shows a non-numerical switch, the searching operation of which isin part controlled by an operator. The circuit is taken into use fromthe bank contacts of a selector level 'fills a level or uses only partof a level.

a and b are looped causing the operation of relay A. Relay A closes apossible circuit for the relay P leading to a wiper, the bank contact ofwhich, in the home position, is connected to a source of batterypotential if any of the outlets fromthe switch are available. Thissource of potential is 'sufiicient to cause the operation of relay Pwhich is a relay of the two-winding type and which is adapted toshort-circuit one winding on its operation in order to reduce thepotential on the bank contact after operation. Relay A also closes acircuit for relay C which also has two windings, one of which isnormally shortcircuited, in which circumstances the relay C is slow tooperate. If the relay P does operate it will open the circuit of relay Cand close the circuit of relay L, which will look over its ownmake-before-break contacts. Relay L closes the driving circuit for theswitch from ground connected to the bank contacts and the switch willcontinue to run through its interrupter contacts until it reaches anoutlet not marked busy. At this point the relay K operates in serieswith the rotary magnet and switches the incoming leads through to theoutlet. The relay K is maintained operated on the third wire. If all theoutlets are engaged the relay P fails to operate and the relay Coperates, connecting a flashing signal from lead FL to the fourth wire dwhich will cause a supervisory lamp at the operators position to flashintermittently. Relay C also I connects the high resistance relay HR inseries with relay P to the group control wiper so that when source ofpotential is connected, indicating that one of the outlets has becomefree, the relay I-IR only will'operaten Relay HR in operating removesthe flash. from the (2 wire which is now connected to a flicker signalin series with the second winding of relay C back to the operator. Theoriginal operating circuit of relay C is now switched over to aninterrupted battery which is so timed in relation to the flicker signalthat the relay is alternately maintained operated over one winding andthen the other. When the operator wishes to commence the searchingoperation, the circuit over the fourth wire is opened, causing relay Cto release.

The low resistance circuit for relay P is reconnected and when the relayP operates the switch hunts as already described. If two operatorsattempt to take a free outlet simultaneously only one P relay willoperate, but in the other circuit relay HR will release, relay C willreoperate and flashing signal will be reconnected to the cl wire. When afurther outlet becomes free the relay HR will operate again and theoperator can make a further attempt in response to flicker.

Fig. 2 shows the circuit of a two-motion se lector which is arranged tobe set by either one or two digits according as the group required RelayC, not shown, is arranged in the normal manner to operate with eachimpulse. This relay is slow to release and controls the release relay CCwhich is also slow to release. When relay C releases at the end of thefirst (or second) digit a circuit is closed through the operatingcontacts of relay CC to the congestion relay P and if the relay Poperates to battery via the group congestion circuit GCC, the drivecircuit of the rotary magnet RM, in series with left-hand winding ofrelay and on seizure the negative and. positive wires 'manner." When theswitching relay H '(not shown) operates its contacts hI switch throughlead d. If the relay P fails to operate before the relay CC releases,the circuit will be completed.

jing lead FLA to the relay FL which in turn conmeets the relay SCintermittently to the fourth wire, thereby giving a flashing signal tothe operator. When the operator restores her listening key, relayv SCoperates and locks, releasing BF so that busy flash is removed. RelayCC, in its normal position, also closes the circuit for the highresistance relay HR to the group control contact in series with P. Whenan outlet becomes free relay HR alone operates and switches over thecircuit FL at hrl to the flicker ground via FLI thereby causing avquicker train of impulses to be sent back over the fourth wire toflicker the operators lamp. During these interruptions the circuit forthe relay SC is maintained operated over its locking circuit. When theoperator wishes the switch to attempt a search, the circiiit of therelay SC is opened or high resistance isinserted therein by throwing thelistening key and the relay SC recloses the circuit for the relay BF.With both BF and HR operated, the relay CC reoperates via hT5, M3 andallows a further test to be made by the relay P; The circuit of therelay HR is opened by the relay CC and if relay P fails to operatebefore CC also releases, the flashing signal is reintroduced as alreadydescribed.

Referring now to Fig. 3, which represents the equipment at both ends ofa both-way junction group, an operator setting up a call in a wanteddirection, is connected via a group selector GS to a non-numerical trunkselector TS, which is of the kind shown in Fig. 1 and is adapted to giveaccess to an idle both-way junction circuit J C.

If all the outlets from TS are busy, connection is made to a directiondelay recorder DR associated in multiple with all TS circuits givingaccess to the same group of toll junctions or trunks. Associated withall the DR circuits is a delay counter circuit DLC comprising a switchRI which is stepped round at a given speed whenever congestionconditions exist and has a'position individual to each TS circuit.During each revolution of switch RI, a switch R2 of each DR is given atleast one step for each of its associated TS circuits awaiting a freeoutlet. The number of steps taken by R2 in this way is determined by arelay DP individual to DR. 'The compensator DRC comprises a switch R5which records the number of times those junctions of the group inquestion, on becoming free, are taken into use consecutively at the farend, and accordingly varies the rate of stepping of a second switch R3of DR for a purpose which will be explained shortly. The circuits JC ofa group are adapted to be individually connected to the corresponding DRby an associated circuit AC. This connection is automatically made eachtime a junction falls free irrespective of the existence of congestionconditions in the group. Each JC comprises a switch R4.

When a junction falls free, the JC circuits at both ends are connectedto their DR circuits and the switch R4 at the outgoing end for the calljust terminated is stepped, causing pulses of two different frequenciesX, Y to be sent consecutively. On receipt of this signal R4, at theincoming end, sends back a pulse of the Y frequency and the outgoing R4returnsa further Y pulse.

a trunk line is available.

The incoming and outgoing circuits are now ready to signal the amount ofcongestion recorded to each other. "If calls are waiting at the incomingend, a first congestion pulse of 'Y frequency will be sent, and at thesame time, the switch R3 of the incoming DR will be stepped forwardatleast one step. At the outgoing end, on receipt of this pulse, a Ypulse is sent back and the corresponding R3 is also stepped, Originally,whenno congestion existed, R2 and R3 of DR were both at normal. R2 hasbeen stepped forward over a number of contacts determined by the numberof TS circuits of the group awaiting a free junction, and by the lengthof time these TS circuits have been in the waiting condition. RI takesone step per half-second and is a fiftypoint switch, and. therefore R2has taken one step per waiting TS every twenty-five seconds- R3, whenstepped as JC sends a Y congestion pulse, takes at least one step tocatch up with R2.

R3 takes four steps per Y congestion pulse'normally, but is controlledby DRC to take only two stepsor one step if the other exchange has takenthe last two, or three, junctions falling free respectively.

The incoming and outgoing ends continue to exchange Y pulses untilswitch R3 at one end catches up with its-R2, when no more Y pulses Willbe sent from that end, and the "other end .still having congestionrecorded, and receiving no further Y pulse, allows the TS circuits toflicker the operators to inform them that a junction' is available.

Congestion records at both ends willthen be built up again.

It will be seen that the end which has not taken the last two or morejunctions, counts off its congestion record by means of switch R3 at amuch slower rate than the other end, and therefore is more likely to getan available junction. DRC of course allows switch R3 to resume itsnormal stepping rate after a junction has been taken,

circuits are engaged. Relay C remains operated during the waitingperiod. Relay HR is connected to a wiper of the switch by C and willoperate as soon as a trunk becomes available. "The operation of therelay HR will release 0. Relay HR removes the flashing signal andsubstitutes a flicker thereby indicating to the operator that The factthat relay C is operated in any one trunk selector circuit indicatesthat an. operator is waiting for a trunk line.

-It follows that an indication of the traflic waiting in any directioncan be obtained by measuring the number of C relays which are operatedsimultaneously and the time period during which they remain operated.This measurement must be made independently for each direction and thedirection delay recorder DR is, therefore, associated only with a groupof TS circuits giving,

access to junctions in one direction only.

The actual measurement is controlled by the delay counter Fig. 6whichmay be common to a number of directions. place as follows:

Relay C in the non-numerical trunk selector Fig. 4 connects groundthrough a decoupling resistance to relay ST of the direction delayrecorder, Fig. 5, which in operating closes the obvious circuit for acongestion meter CM indicating the number of occasions on which alltrunk lines are engaged. It also closes the obvious circuit for therelay CST of the delay counter Fig. 6.

Relay CST in operating connects the magnet RMI of the switch Rl to ahalf-second pulse supply causing the wipers of the switch to stepforward one step every half second.

Two wipers Tm] I, Tml2 are connected together, one set of bank contactsbeing connected individually to C contacts of the trunk selectors, theother set of bank contacts being strapped together according todirection and connected to relays DP in the corresponding directiondelay recorders, Fig. 5.

Every time the wipers of the switch RI pass over contacts correspondingto a trunk selector TS of the group associated with DR, Fig. 5, in thewaiting condition, a ground connection will be passed to the relay DP inthe delay recorder. Relay DP in operating closes the obvious circuit formagnet RM2 of the switch R2, which advances its wipers accordingly.

The switch R2 has only one level of contacts which are connected to acorresponding set of contacts in the switch R3, which also forms a partof the direction delay recorder. The switch R3 is advanced only when atrunk circuit becomes free and it is the function of the switches R2 andR3 to count off between them the amount of delay which has beenstoredsince the last trunk circuit became free. 7

Relay PC which is connected to the wiper rm3l is arranged to operatewhen the switches R3 and R2 are approximately in phase.

The wipers of the switch R3 are advanced in stages until the relay PCeventually operates indicating that the switch R3 has caught up theswitch R2. The number of steps of the switch R3 comprising the stage maybe varied by the compensator, Fig. 9, as described subsequentlyaccording to the circumstances.

When a trunk circuit is about to fall free because the call for which ithas been used is ended, the release is made dependent upon the directiondelay recorder and for this reason the both-way trunk line circuit Fig.7 must be associated with the recorder. This association is performed bya group of relays K shown in Fig. 8, the connecting function of one ofthe K relays being shown in Fig. 7.

It will be appreciated that due to the releasing times of relays and thepossible differences in exchange voltages the both-way circuit may nottend to become free simultaneously at both ends, and should it happenthat two junctions of a group become free at approximately the sametime, the associating relays may be caused to operate in such a way thatthe direction delay recorders at opposite ends become individuallyconnected to different junctions and are unable to signal to oneanother. In order toavoid confusion arising in this way, one of the twoterminations acts slightly diiferent from the other, it being adapted tocancel the first association and make a second association when theconditions indicate that the direction delay recorders have beenassociated with different trunk lines.

The relays KI, K2, K3, etc., are provided one Detailed operation takesper trunk line circuit and one of these relays and v its contacts areshown on Fig. 7.

The pairs of terminals AKI, AK2; AK3, AK4, Figs. 7 and 8, are particularto different junction circuits JC. A potential is connected to terminalAKI, for instance, when the correspond ing trunk line is about torelease after completing an outgoing call, and a similar potential isplaced on the terminal AK2 when the same circuit JC is about to releaseafter receiving an incoming call. At one end of the trunk linetheterminals AK! and AK2 are connected together, but at the other end theyare wired separately in order to avoid cross connections.

When a ground potential is connected to: a point such as AK3, Fig. 8, atthe end of an outgoing call, the relay K2 will operate through contactsMI, 1092, k22,kw| to battery potential through relay KY. Relay K2 inoperating closes its make-before-break contacts making itselfindependent of the break contact 71:22. Ground potential now beingplaced on terminals AKI or AK at the termination of other outgoing callswill not cause the operation of the relay KI or K3 because the operatingcircuit is opened at the contacts 7022.

When the pairs of terminals AKI and AK2, AK3 and AK4, etc. are connectedtogether, and the K relays, Fig. 8, need have no right-hand windings,only one K relay can be operated at a time and this relay will remainoperated until the trunk line circuit removes the ground potential.

When the corresponding terminals are not wired together but wiredseparately, the second terminal is Wired through a second Winding of theK relay and through a relay KW tothe battery potential through relay KY.With this arrangement a K relay can become operated on its secondwinding even if another K relay is already operated on its firstwinding. Furthermore, the operation of the relay KW in series with saidK relay will open the circuits of the first windings of all K relays sothat any K relay, which was previously operated via an outgoingterminal, is caused to release.

The K relay at the incoming end of a-junction about to come free cannotoperate until a signal has been received from the outgoing end after thelatter has been connected to its DR. It will be seen that with thisarrangement if two trunk lines which have been used in differentdirections are released simultaneously and both outgoing ends makeassociation with their corresponding direction delay recorders and, inconsequence, initiate the releasing signals, a second K relay will beoperated over its second winding at the one end to disassociate thedelay. recorder at that end from the toll line to which it is connectedand reassociate it with the toll line which has received an incomingsignal.

Turning now to Fig. 7, the relay A is bridged across the conversationalleads from the local subscriber and is designedv to operate so long asthe callingsubscribers receiver is off the hook. The outgoingconversational leads are not shown. Relay A operates B, which is of theslow to release type. Relay C then operates and locks up so that thetoll line circuit is not. automatically released when the callingsubscriber clears.

Considering first the case in which the trunk line circuit is used foran outgoing call. The operation of relay B closes at contacts b-l thecircuit for the magnet RM4 of switch R4 through its interrupter springs,the first bank QQntact and wiperrmfl causing the switch to advance toposition 2. The. relay SC isoperated .(YlfljCOIltflCl; a2 of relay A) onall outgoing calls and the contact 30! closes a circuit for magnetRlVI4;"via its interrupter springs, sol, bank contacts, wiper rm43 toground. This circuit is maintained until wiper rm44 reaches its firstcontacts, which is the twenty-sixth position of the switch. The switchremains in this position during the course of conversation but at thecompletion of conversation when the relay B releases the circuit for themagnet RM4 is completed through wiper rm42, the break contact b2, thecontacts gl and the wiper rm44 to ground. The switch advances its wipersone step to position 21 in which position ground is connected to theterminal AKI through contacts b3, ro l, 302 and wiper rm48. If thedirection delay recorder is not already associated with a trunk linecircuit, the relay K will operate and. close at contact kl the circuitthrough the wiper rm42 for the magnet RM4, which advances the switch toposition 28. In this position the toll. line circuit sends the initialrelease signal to the distant end. It will be understood that thesignaling over the toll line may be vcarried out in a number ofdifierent ways, e. g. by the use of two or more voice frequencies placedon the line or by the use of a single frequency of various duration orby means of direct current signals. In this description it has beenassumed that signaling is undertaken by means of two voice frequencies,but the sources of frequencies and their connections to the outgoingjunction leads are not shown as they may be of any known type. When theswitch R4 reaches position 28, that is, the third position in banksrm42, 44, 46 and 48, the circuit is closed for the relay FX throughwiper rm46 contacts kl I, 302, rcl, b3. FX in operating connects the Xfrequency to the outgoing line. In position "the magnet RM4 is connectedthrough its interrupter springs and rm42 to a half-second pulse supplycausing the switch to advance one step per pulse to positions 29, 30, 3|and then 32. In positions 28, 29, 30 and 3| relay FX is maintainedoperated so that as a result the X frequency remains on the line thewhole of this period: In positions 32 and 33 the circuit for the relayFX is open, but the circuit for the relay FXY is closed so that in thesetwo positions the Y frequency is connected over the lines. Theinterrupter circuit for the magnet RM4 is completed wiper rm42 and thewipers are advanced to position 34. The toll line circuit now awaits asignal from the distant end of Y frequency and when this arrives,frequency-responsive relay Y not shown connects ground through contactsb3, rcl, s02, Icll, wiper rm46, contact yl to the terminal XZO, which isconnected .to the direction delay recorder shown in Fig. 5, through onewinding of relay KB and the relay Z, which both operate. 7

Relay Z at 2| opens a possible circuit for the magnet RM3, and contacts:cbl close the obvious circuit of the relay X. When the Y pulseterminates, the relays KB and Z are both released. The relay 163 isgauged with a heavy spring pressure so that it operates relativelyslowly and releases quickly. The relay Z on the other hand hasrelatively light-pressure and operates quickly and releases relativelyslowly. During the period between relays KB and Z releasing, a circuitis closed from ground, e2, :rl, :rb2, to the terminal MAG, which isconnected via the corresponding terminal of the both-way trunk circuit,through k2, and rm42 to magnet RM4; This signal causes the switch R4 toadvance a step and in the following position a circuit is reestablishedfor the relay FXY which again applied Y pulse over the trunk line.Switch R4 does not remain for any length of time .in this positionbecause the circuit is at once closed through the wiper rm42 whichcauses the wipers to advance a further step.

In the next position of the switch, the circuit for the relay FXY ismaintained until relay X releases and connects ground at X2 to terminalZG which is extended through contact 103 through the bank contact andwiper rm42 to the magnet RM4 causing the wipers to advance to position31. In this position the circuit awaits for a further Y pulse from thedistant end which, as already described, causes the operation of therelay KB and Z and, at the termination of the Y pulse, ground isconnected over the terminal MAG which advances the wipers of the switchR4 to position 38. In this position ground is extended through rm 46,contacts pol, and terminal X132 to the second winding of relay XB, Fig.5, which is operated thereby, and in parallel through the metalrectifier, terminal X80 and contacts k4 to relay FXY. The operation ofthe relay FXY reconnects the Y frequency to the trunk line. Theoperation of relay XB, which looks up through contacts $113 and 22 toground, causes the operation of the magnet RM3 through contacts :23, 2|and :rb4. Relay XB also closes at xbl, the circuit for relay X which inoperating opens the short circuit across the interrupters ofRM3at m3 andcauses the switch to take a step. The switch R3 continues stepping untilthe circuit is closed for the relay Z through the bank contact and wiperrm32 and the contacts 1'4.

Relay Z in operating opens the circuit of the magnet RM3, opens at 22the holding circuit of the relay KB and closes through the contactsxl,a:b2 the circuit for RM4, which is therefore caused to advancethrough both positions 38 and 39 into position 40.

If the relayPC had been operated when the switch reached position 38;via stl, rm3 I, rm2l .to earth, because the switches R2 and R3 were inphase, relays KB and FXY would not have operated, Y pulse would not havebeen connected to the trunk line and relays CA, Fig. 9, and RC wouldhave been operated via Jxyl, k5, pcl energized, rm46 to earth.

Relay RC is arranged to look over contacts b2. Switch R4 returns homethrough contacts 102 and rm to ground. Relay RC indicates that the tollline circuit should receive an incoming call and in consequence does notpermit the condition ofthe group .test terminal to be altered. I

Assuming that the relay PC is not operated and that the switch R4 wasadvanced to position 40, the circuit would again await the receipt of Ypulse which again causes the operation of relays X8 and Z, and again atthe termination of the Y pulse the wipers advance to position 4|. If therelay PC is still not operated the relays KB and FXY will be againoperated in positions 4| and 42 and the wipers step forward to position43 Assuming now that the distant end does not reconnect the Y pulse, therelays X3 and Z will not operate but-the circuit will be completed fromthe magnet RM4 through the wiper rm42, contact k2, terminal MAG, 152,Fig. 5, .rl, makebefore-break contacts mbl, left-hand winding of therelay MA to ground.

Relay MA being of relatively high resistance, the magnet RM4 will not beoperated but the relay MA will operate and close the contacts mal andthe half-second pulse supply to the second winding of relay MA and therelay MB. When this supply is connected the relay MB operates and. therelay MA remains operated for the duration of the pulse. On thecompletion of the pulse, relay MB remains operated on its upper windingthrough contacts ml)! in series with the magnet RM4, but MA is released.When ground is again connected to the pulse supply the circuit iscompleted through the contacts mal, 717122 for the relay MC and if bythis time Y pulse has not been received, relay MC operates and connectsground via mcl, st4 to the MCG terminal through contacts 106, Fig. 7, tothe lower winding of relay SC, which operates. Relay SC closes at $03 alocking circuit through b2, rm to ground. Contacts s04 open the lockingcircuit of relay C which in releasing closes a homing circuit; RM4,interrupter, sci, cl, rm44, ground. When the switch reaches home, groundis removed from the terminal AKI, and relay K is released together withthe direction delay recorder.

It will be understood that the operation of relay SC, indicating thatthe trunk line should be used for an outgoing call, may take place atposition 40, 43, 46, etc. and similarly the operation of the relay RCmay take place at position 38, 4|, 44, etc.

If the trunk line circuit is associated with the direction delayrecorder on an outgoing connection and the relay KW becomes operatedbecause the distant end recorder is associated with the different trunkline, a circuit is completed through contacts k! and g2 for the relay G,which is arranged to lock up. The contacts gl and subsequently thecontacts 93 and g4 advance the wipers of the switch R4 through normal toposition 26 in which position the circuit for the relay G is opened.Relay G in releasing closes the circuit for the magnet RM4 through1'm42, 112, Q], rm44 causing the switch to advance to position El whenreassociation with the direction delay recorder will take place when thelatter circuit becomes available.

Considering now the case of an incoming call, relays B and C of thetrunk line circuit are operated and switch RM4 is advanced to position 2but no further since SC is not energized. It remains in this positionthroughout the conversation but on release a Y pulse is received fromthe distant end.

Relay Y closes at 1 2 the circuit for the magnet RM4 and switch R4 isadvanced to position 3. In position 3 ground is connected through wiperrm4l to terminal AKZ to cause the association with the direction delayrecorder to take place. When the Y pulse is completed and the relay Koperated, groundis connected through 1/3, Icl and rm ll to advance theswitch to position 4.

In this position the relay FXY is operated and the return Y pulse issent to the distant trunk exchange. The wipers are advanced by directearth on 111241 to position 6 where a. further Y pulse signal isexpected from the other exchange and when it is received causes theoperation of relay X13 and Z, Fig. 5, in the manner already described.

In positions I and 8 the operation of relay X5 is made dependent on thecondition of contacts pol as before so that, in this and subsequentsen-ding positions, the controlling switch R3 is advanced, and as soonas the switch R3 is in phase with the switch R2, no further congestion Ypulses are sent.

If no further Y pulse is received from the distant exchange, relays MA,MB and MC are operated as already described. The subsequent operation ofrelay SC results in the trunk line being made available for an outgoingcall. If, on the other hand, relay PC is operated resulting in theoperation of relay RC, the trunk line is prepared to receive a call fromthe distant end.

It may be arranged that if the outgoing end has no calls waiting thesecond signal sent in positions 35 and 36 will be of X pulse rather thanof Y pulse; such an arrangement can be accepted at the incoming end bywiring position 6 to position 9 through the back contact of a relay RX(not shown) responding to the X pulse. It will be arranged that shouldthe X pulse be received in position 6 the relay SC can be operatedimmediately.

During the period when the trunk line is associated with the directiondelay recorder and relay KY is operated, the possible circuit for theswitch R2 is opened at contact kyl and on this account the circuit forthe relay PC cannot be caused to open instantaneously.

Reference has already been made to the fact that in certaincircumstances there may be a preponderance of trafiic in one directionand in consequence over a relatively long period there will be a largenumber of Waiting callsin one direction. Under these conditions it maybe difiicult for a call in the reverse direction to get access. In orderto eliminate this possibility a compensator circuit is proposed as shownin Fig. 9. It is the purpose of this circuit to vary the connection viathe bank contacts associated with the wiper rm32 so that the size of thestages of movement of said wipers, when sending congestion pulses, is inpart dependent upon the direction in which the majority of the trafficis flowing.

As an example, the contacts associated with the wiper rm32 are dividedup into three groups. Contacts I, 3, 5, I, 9 etc., are connectedtogether and wired to terminal CX. Contacts 2, 6, l0, l4, etc. areconnected together and; wired to terminal CY, contacts 4, 8, l2, etc.are likewise connected to terminal CZ, and also direct to the right-handwinding of relay Z.

Relay CA, Fig. 9, is connected in series with the operating winding ofrelays RC of the various trunk line circuits and every time that a trunkline is released and assigned for an incoming call relay CA willoperate. Relay CA closes the obvious circuit for the switch R5 which iscaused to take one step for each successive junction assigned forincoming use.

Contacts 3, 4, 5, 6, I, B, 9, I associated with wiper rml are commonedtogether and connected to the terminal CZ. Corresponding contactsassociated with the wiper rm52 are connected to terminal CY and contacts4, 5, 6, 1, 8, 9, l0 associated with wiper rm53 are connected to theterminal CX.

On the second successive incoming call switch R5 reaches position No. 3and the terminals CY and CZ are commoned together and because of thisthe relay Z in the direction delay recorder is operated after only twosteps instead of four steps of R3.

If a further incomingcall is received, R5 advances another step and inthis .position terminals CX, CY and CZ are all commoned together. RelayZ operates after every one step of R3. On the use of any junction in'the route for an outgoing call a relay MC (not shown) will operate andcomplete the circuit through wiper rm54 to drive the switch to a furtherhome position, from whence the process will be repeated.

What is claimed is:

1. In a toll switching system, the combination with a plurality ofoperators positions of a plurality of link circuits each-comprising afinder, an incoming line group available for connection with all of saidlink circuits, an allotter for operatively associating any link with anyposition, means responsive to the existence of a calling condition onany line of said incoming line group for operating any idle link toconnect its associated finder with said calling line, and meansresponsive to an operation at anyone of said positions for operatingsaid allotter to associate the link extended to the calling line withthe position at which said operation has taken place.

2. In a toll switching system, the combination of two offices connectedby a plurality of two-way trunk lines, a selector circuit at each ofiicehaving access to said trunk lines, means at each oflice operativelyassociated with each selector for determining and recording the timeinterval during which all of said trunk lines are busy, means at eachofiice operatively associated with each selector for determining andrecording the time interval during which each of said selectors has been'waiting for a free trunk line to establish a call in its own direction,means responsive to a line becoming free for signaling over said linethe selector delay at each oflice, and means for allotting said freeline to the ofiice which had the longest selector delay.

3. In a telephone system, two ofiices, a group of two-way trunk circuitsextending between said ofiices, switching means at each office forseizing idle trunk circuits,'and means at each ofiice controllable inaccordance with the number of calls awaiting completion at each oiliceand the aggregate waiting period of such calls for allocating an idletrunk circuit for the use of the oflice in which the trafiic congestionis greater.

4. In a telephone system, two oflices, a group of two-way trunk circuitsextending between said ofiices, switching means at each ofiice forseizing idle trunk circuits, means at each oflice for recording duringperiods when no idle trunk circuits are available the aggregate waitingtime of calls awaiting an idle trunk circuit, and means at each oflicecontrollable jointly by the recording means at both oflices fordetermining whichfoffice may use an idle trunk circuit for an outgoingcall when it becomes free.

5. In a telephone system, two ofiices a group of two-way trunk circuitsextending between said o'fiices, switching means at each ofiicev forseizing idle trunk circuits, means at each oflice for recording duringperiods when no idle trunk circuits are available the aggregate waitingtime of calls awaiting an idle trunk circuit, and means at each officecontrollable jointly by the recording' means at both oflices forallocating a trunk circuit when it becomes idle to the use of the ofiicewhose recording means indicates the greater trai'fic congestion.

.6. In a telephone system, two oflices, a group of two-way trunkcircuits extending between said ofiices, switching means at each'ofiicefor seizing idle trunk circuits, means at each office for, recordingduring periods when no idle trunk circuits are available the aggregatewaiting time.

of calls awaiting an idle trunk circuit, and means at each ofiicecontrollable jointly by the recording means at both ofiices responsiveto a trunk circuit becoming free for indicating at the oifice wherethegreater traffic congestion exists that the free trunk circuit is to beused on an outgoing call .and :for indicating at the other ofiice thatthe free trunk circuit is to be reserved for an incoming call.

7. In a telephone system, two oflices, a group of two-way trunk circuitsextending between said offices, switching means at each ofiice forseizing idle trunk circuits, means at each oflice for recording duringperiods when no idle trunk circuit is available the aggregate Waitingtime of calls awaiting an idle trunk circuit, means at each ofiiceoperative when a trunk circuit becomes available for transmitting signalimpulses to the other ofiice, and means at each ofiice jointlyresponsive to the recording means of that office and to the impulsesreceived from the other oflice for allocating said idle trunk circuitfor an outgoing call to the use of the office in which the trafficcongestion is greater.

8. In a telephone system, two ofiices, a group of two-way trunk circuitsextending between said ofiices, switching means at each oflice forseizing idle trunk circuits, means at each ofiice for recording duringperiods when no idle trunk circuits are available the aggregate waitingtime of calls awaiting an idle trunk circuit, means at each ofiiceoperative when a trunk circuit becomes available for transmitting signalimpulses in alternation over said idle trunk circuit to the otherofiice, and means at each office jointly responsive to the recordingmeans of that oflice and to the impulses received from the other ofiicefor allocating said idle trunk circuit for an outgoing call from theofiice in which the trafiic congestion is greater and for an incomingcall at'the office in which the trafiic congestion is less.

9, In a telephone system, two ofiices, a group of two-way trunk circuitsextending between said ofiices, switching means at each oflice forseizing idle trunk circuits, a first recording switch at each ofiice,means at each office operable during periods when no idle trunk circuitsare available for setting the associated recording switch in accordancewith the aggregate waiting time of calls awaiting an idle trunk circuit,a second recording switch at each office, means at each ofiiceoperativewhen a trunk circuit becomes free for transmitting signalimpulses to the other office for setting the second v recording switchat the other ofiice, and means operative when the recording switches ofeither ofiice are in substantial phase relationship for transmitting asignal to the other ofiice indicative that the free trunk circuit may beused at such ofiice for an outgoing call.

10. In a telephone system, two oflices, a group of two-way trunkcircuits extending between said offices, switching means at each ofiicefor seizing idle trunk circuits, a first recording switch at eachofiice, means at each ofiice operable during periods when no idle trunkcircuits are available for setting the associated recording switch inaccordance with the aggregate waiting time of calls awaiting an idletrunk circuit, a second recording switch at each office, means at eachofiice operative when atrunk circuit becomes free for transmittingsignal impulses to the other ofiice for advancing the second recordingswitch at the other ofiice a predetermined amount in response to eachimpulse, means operative when the recording switches of either officeare in substantial phase relationship for transmitting a signal to theother ofiice indicative that the free trunk circuit may be used at saidother office for an outgoing call, and means at each office effectivewhen the other ofiice has been given precedence for a predeterminednumber of successive outgoing calls for reducing the amount ofadvancement of the second recording switch thereof in response toimpulses from the other oifice whereby said ofiice is given precedencefor completing an outgoing call.

11. In a telephone system, two oflices, a group of two-way trunkcircuits extending between said ofiices, switching means at each oificefor seizing idle trunk circuits, a first recording switch at eachofiice, means at each oflice operable during periods when no idle trunkcircuits are available for setting the associated recording switch inaccordance with the aggregate waiting time of calls awaiting an idletrunk circuit, a second recording switch at each oifice, means at eachofiice operative when a trunk circuit becomes free for transmittingsignal impulses to the other office for advancing the second recordingswitch at the other ofiice a predetermined amount in response to eachimpulse, means operative when the recording switches of either officeare in substantial phase relationship for transmitting a signal to theother office indicative that the free trunk circuit may be used at saidother office for an outgoing call, and means at each office efiective inresponse to the allotment in succession of difierent predeterminednumbers of available trunk circuits to the other oilice for outgoingcalls for successively reducing the amount of advancement of the secondrecording switch thereof in response to the impulses from the otheroffice whereby said office is given precedence for completing anoutgoing call.

12. In a telephone system, two oflices, a group of two-way trunkcircuits extending between said ofifices, switching means at each omcefor seizing idle trunk circuits, trafiic congestion recording means ineach office, and means in each office operative in response to a trunkcircuit becoming available for associating the recording means of eachof said ofiices with the opposite ends of said available trunk circuit,

13. In a telephone system, two ofiices, a group of two-way trunkcircuits extending between said ofiices, switching means at each omcefor seizing idle trunk circuits, traffic congestion recording means ineach office, and means in each office operative in response to two trunkcircuits becoming available substantially simultaneously for associatingthe recording means of each of said oflices with the opposite ends ofone of said available trunk circuits.

14. In a telephone system, two oflices, a group of two-way trunkcircuits extending between said ofiices, switching means at each officefor seizing idle trunk circuits, means "at each office for recordingduring periods when no idle trunk circuit is available the aggregatewaiting time of calls awaiting an idle trunk circuit, means at each endof each trunk circuit individual thereto operative when a trunk circuitbecomes available for transmitting signal impulses over said trunkcircuit to the other office, and means at each office jointly responsiveto the recording means of that office and to the impulses received fromthe other ofiice for allocating said idle trunk circuit for an outgoingcall to the use of the office in which the traffic congestion isgreater.

15. In a telephone system, two ofiices, a group of two-way trunkcircuits extending between said offices, switching means at each oflicefor seizing idle trunk circuits, a trafic congestion recorder in eachoffice, said recorders each comprising a first recording switch operableduring periods when no idle trunk circuits are available for recordingthe aggregate waiting time of calls awaiting an idle trunk circuit, anda second recording switch, means at each end of each trunk circuitindividual theretoand operative when a trunk circuit becomes availablefor associating the end of said trunk circuit at each oflice with thetrafiic congestion recorder thereat and for transmitting signal impulsesto the other oifice for setting the second recording switch at the otherofiice, and means operative when the recording switches of either ofiiceare in substantial phase relationship for transmitting a signal to theother office indicative that the free trunk circuit may be used at saidother office for an outgoing call.

ESMOND P. G. WRIGHT. GEOR

